Troubleshooting Tips for a Furnace That is Not Blowing Hot Air

Nothing can be more frustrating than having a furnace that is not able to blow hot air in the cold winter season. In many cases, this may be something easy to fix by yourself.

Furnace Not Blowing Hot Air? 5 Potential Reasons Behind the Issue

1. Thermostat Issues

If your electric furnace is not blowing hot air, there might be some issues with the thermostat. Here are some of the common problems related to a faulty thermostat.

  • Low battery

    Sometimes the issue might be very straight forward like a low battery in the thermostat. If your thermostat runs on a battery unit, you need to check regularly if the battery is dead. Such batteries tend to send faulty temperature reading. This problem is especially common in older units. Even a low battery can malfunction your thermostat. In such cases, replacing the older batteries can solve the issue.

  • The fan is “on” all the time

    Keeping the fan setting to “on” is a common mistake that results in the furnace blowing cold air. Heaters are not set to pump hot air continuously. Once the optimum temperature set by you is reached, it will take a break until the temperature again falls below the set temperature. However, in case the fan is set to be "on", it will start blowing cold air during the downtime. To avoid this, make sure you set the fan to "auto" so that it will blow hot air when needed.

  • The thermostat might not be installed properly

    Your thermostat could be malfunctioning if you missed something while installing the thermostat yourself instead of calling an HVAC professional. You could have installed a new thermostat that is not compatible with the existing heating system. In such cases, it is best to get professional help to install it correctly as soon as possible.

Also read: How to Use Your Heat Pump Right to Save Money

2. Issues with the furnace filter

A dirty, clogged filter can restrict the airflow to your furnace which limits its ability to evenly distribute warm air in your home. Cleaning the filter could solve the issue.

3. Problems with condensate lines

The condensate lines always need to be kept clean and open. The condensate lines are regularly draining water away. It causes the lines to accumulate dirt, and get clogged. The excess buildup of dirt could lead the system to start blowing cold air and eventually shut down. Get a regular inspection done by HVAC professionals to ensure that the condensate lines are completely free of dirt and grime.

Also read: What Causes Furnace to Turn On and Off Frequently?

4. Gas valve problems

A gas furnace needs to be cleaned regularly. Dirt and debris can cause the gas valve to shut down or malfunction. If you've an old gas furnace, the gas valve could have worn out, causing the furnace to blow cold air. Scheduling regular furnace maintenance can avoid such issues.

5. Burner issues

When the burners of your furnace are clogged, there won't be enough fuel for your furnace to keep blowing out hot air. In such cases, if your fan is still running, it could cause the system to blow out cold air, instead.

Also read: Furnace Duct Cleaning: Know About Their Pros and Cons

Troubleshooting Furnaces Not Blowing Hot Air

Here are some furnace troubleshooting tips you can try if your heater isn't blowing hot air. Read more:

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Comment by Paul Raymer on January 30, 2020 at 11:37am

My furnace is sourced with a hot water loop from the water heater.  I kept turning up the water heater temperature until the temperature/pressure relief valve started blowing water out onto the basement floor.  After a lot of air and pipe temperature measurements and thermostat connection testing (new T-stat installed) and a bunch of other stuff, it appeared that the circulating pump in the furnace had given up the ghost.  Hot water was simply not circulating through the coil in the furnace.  The shaft of the impeller in the pump had shattered.  And somewhere through the years water had leaked into the electrical connections destroying them.  We ended up mounting an extra pump on the outside of the air handler.


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